Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02674009 2009-07-27
Line Voltage Thermostat With Energy Measurement Mechanism
FIELD OF THE INVENTION
[0001] The present invention relates to thermostats, and more particularly, to
a
thermostat for a line powered device or apparatus and including an energy
consumption
mechanism.
BACKGROUND OF THE INVENTION
[0002] Line voltage thermostats are known in the art for controlling heating
equipment,
typically baseboard heaters or convection heaters. The thermostat can be
adjusted to a
temperature set point such that, when the temperature in the conditioned space
reaches
the set point, the thermostat turns off the heating equipment. The thermostat
continues
to monitor the temperature in the space and when it drops below the set point,
the
thermostat turns on the heating equipment until the desired temperature is
achieved.
[0003] Advances in the art have given rise to programmable thermostats and
thermostats with additional functionality. Programmable thermostats allow a
user to
program the thermostat to automatically change the set-point temperature
during various
times during the day and/or week. Thermostats now also include the capability
for the
user to temporarily override the temperature setting and/or permanently hold
the: set-
point temperature.
[0004] While existing advances in the art have resulted in thermostats and
programmable thermostats with increased functionality, there still remains a
need for
improvements in the art, particularly, in the area of power consumption
determination
and management.
[0005] More specifically, there is a need to provide a user with accurate
energy
measurement for a line powered device and an estimated monetary cost for the
energy
used. Furthermore, it is desirable to provide a user with a warning if the
estimated
energy cost exceeds a predetermined limit.
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[0006] Further still, there is a need to detect a malfunction or unsafe
operating condition
in a line powered device and further provide a user with a visual or auditory
warning.
Exemplary malfunctions or unsafe operating conditions in a line powered device
include
open circuits, overloading or the like.
SUMMARY OF THE INVENTION
[0007] The present application is directed generally to a thermostat of a line
powered
device or apparatus and according to an aspect includes an energy consumption
calculation mechanism.
[0008] According to one aspect, there is provided a thermostat for a line
powered device
configured for operating in a physical space, the thermostat comprises an
input line for
receiving an AC supply voltage; an output line for providing the AC supply
voltage to the
line powered device; a switch coupled between the input line and the output
line and
being operable in an open state and a closed state; a controller including a
temperature
control component configured to activate the line powered device for a desired
temperature setting by placing the switch into the closed state to provide the
AC supply
voltage on the output line; a sensing mechanism coupled to the input line and
being
configured to sense a line voltage reading and a line current reading; the
controller
includes an input port for receiving the line voltage and the line current
readings; and the
controller includes an energy calculation component configured to calculate a
power
consumption value for the line powered device based on the line voltage and
the line
current readings.
[0009] According to another aspect, there is provided a thermostat for
controlling a line
powered device, the thermostat comprises: an input port for receiving an AC
supply
voltage; an output port coupled to the line powered device for outputting the
AC supply
voltage; a switch coupled between the input port and the output port and being
operable
to connect the input port to the output port to output the AC supply voltage
to the line
powered device; an analog module having a first input coupled to the input
port for
inputting a line current reading, and a second input coupled to the switch for
inputting a
line voltage reading; an analog to digital converter configured with a first
channel for
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converting the line voltage reading into a corresponding digital line voltage
reading and
configured with a second channel for converting the line current reading into
a
corresponding digital line current reading; and a controller having an input
port coupled
to the analog to digital converter and the controller having a component
configured for
calculating a power consumption value based on the digital line voltage and
line current
readings.
[0010] Other aspects and features will become apparent to those ordinarily
skilled in the
art upon review of the following description of embodiments in conjunction
with the
accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Reference will now be made to the accompanying figures which show, by
way of
example, embodiments of the apparatus described herein, and how they may be
carried
into effect, and in which:
[0012] Fig. 1 shows in diagrammatic form a thermostat configured with an
electric
baseboard heater according to an embodiment of the present invention;
[0013] Fig. 2 shows in schematic form an implementation of the thermostat of
Fig. 1
according to an embodiment of the present invention; and
[0014] Fig. 3 shows in schematic form an energy measurement mechanism for the
thermostat of Fig. 2 according to an embodiment of the present invention.
[0015] Like reference numerals indicate like or corresponding elements in the
drawings.
DETAILED DESCRIPTION OF THE INVENTION
Overview
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[0016] Reference is first made to Fig. 1, which shows in diagrammatic form a
thermostat
with an energy measurement or consumption calculation mechanism according to
an
embodiment of the invention and indicated generally by reference 100.
[0017] In the figures, like reference numerals indicate like or corresponding
elements.
[0018] As shown in Fig. 1, the thermostat 100 comprises a display 110 and a
keypad
120. The display 110 and the keypad 120 are mounted in a housing or enclosure
130
and operatively coupled to a control module. A control module 210 according to
an
embodiment of the present invention is described in more detail below with
reference to
Fig. 2. As shown, the thermostat 100 includes an interface 140 for connecting
or
coupling to an electric baseboard heater indicated by reference 102. The
baseboard
heater 102 is implemented in a conventional manner and comprises a heating
element
104 and may include a limit element 106, which is configured to shut off the
heating
element 104 if a safe operating temperature or condition is exceeded. The
electric
baseboard heater 102 receives power from an AC mains supply in a conventional
manner, i.e. with a three terminal electrical connection 108 comprising, Line
1(power),
Line 2 (neutral) and Ground. According to an embodiment, the interface 140 is
coupled
or wired internally to the electric baseboard heater 102 and comprises a two
wire
configuration, with one wire 141 coupled or connected to the power line (i.e.
Line 1) from
the AC mains supply, and another wire 142 providing the power feed for the
baseboard
heater 102. This configuration allows the thermostat 100 to connect directly
to the
electric baseboard heater 102 and function as a control switch to directly
control the
current passing through the electric baseboard heater 102.
[0019] It will be appreciated that while embodiments according to the present
invention
are described in the context of an electric baseboard heater or a line powered
space
heater, the embodiments have wider applicability to other types of line
powered devices
or apparatus.
[0020] Referring to Fig. 1, the keypad 120 is configured with a number of keys
or
buttons that allow a user to select a desired temperature setting, set the
clock, or for a
programmable thermostat, buttons for programming the thermostat, for example,
to one
or more temperature settings based on time. According to another aspect, the
keypad
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120 includes one or more keys to allow a user to enter power consumption
and/or
energy information for the electric baseboard heater 102 (for example, based
on the
marked ratings of the heater). This information can then be provided by the
energy
measurement mechanism, for example, in the context of heater
protections/warnings, as
described in more detail below.
[0021] As will be described in more detail below, the thermostat 100 according
to an
embodiment of the present invention includes an energy measurement mechanism
which is configured to operate with the two wire connection to the electric
baseboard
heater 102 to measure true RMS (i.e. Root Mean Square) values for the voltage
and
current from the AC mains supply, and using the measured values determine
values for
active power and energy consumption. According to another aspect, the
determination of
the values for active power and energy consumption are responsive to user
settings
and/or adjustments.
[0022] Reference is next made to Fig. 2, which shows an implementation of the
thermostat 100 of Fig. 1 according to an embodiment of the present invention,
and is
indicated generally by reference 200. According to an embodiment, the
thermostat 200
comprises two modules: a control module indicated by reference 210 and a power
module indicated by reference 220. The power module 220 is configured to
interface
with the electric baseboard heater 102 (Fig. 1), or other line powered device
for which
energy consumption calculations are required or desired. The control module
210
comprises electronic circuits and components configured to provide the
functionality as
will be described in more detail below.
[0023] The power module 220 interfaces with the AC mains supply and is
configured to
switch the main line current (i.e. the power feed from Line 1 in Fig. 1) to
power the
electric baseboard heater 102 (Fig. 1). The power module 220 is also
configured to
generate a DC supply voltage for operating the control module 210. According
to an
embodiment, the power module 220 comprises a switching device 222 and a shunt
circuit 224. The switching device 222 may comprise an electro-mechanical
device or a
solid state device. According to an embodiment, the switching device 222
comprises an
solid state device and is actuated, i.e. opened/closed, in response to one or
more control
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signal(s) generated by the control module 210. The shunt circuit 224 provides
a current
sensing function and according to an embodiment comprises a resistor 226 which
generates a voltage signal for the control module 210 based on or proportional
to the
line current, i.e. Line 1.
(0024] The control module 210 is configured to control the switching device
222 in order
to power the electric baseboard heater 102 (Fig. 1) and provide a regulated
heat output
according to a setting (i.e. temperature setting or thermostat set point) set
by a user.
According to another aspect and as will be described in more detail below, the
control
module 210 is configured to measure line parameters and calculate energy
consumption
values, i.e. without user intervention. The calculated total usage time and
total energy
are displayed and can be used by the user in a cost calculation or comparison.
[0025] According to an embodiment, the control module 210 comprises a central
processing unit (CPU) 252, a memory module 254, a clock 256, an input/output
module
258, an analog module 260 and an analog-to-digital (ADC) converter 262. The
Liquid
Crystal Display (LCD) module 110 (Fig. 1) is indicated by reference 230 in
Fig. 2, and is
operatively coupled to the control module 210. The keypad 140 (Fig. 1) is
indicated by
reference 240 in Fig. 2, and is operatively coupled to the control module 210.
As shown,
the thermostat 200 includes a temperature sensor 250, which is operatively
coupled to
the control module 210 and provides temperature readings or data for the
physical
space which is being heated by the electric baseboard heater 102 (Fig. 1). The
control
module 210 also includes a power supply circuit (not shown), which taps power
from the
AC input line 141 (i.e. Line 1) and converts it into a DC voltage for powering
the control
module 210 and the associated DC devices and circuitry in the thermostat 200.
[0026] According to an embodiment, the CPU 252 operates under stored program
control, i.e. the CPU 252 executes a program or instructions (e.g. firmware)
stored in the
memory module 254. The program controls the operation of the CPU 252 and
provides
the functions and features associated with the thermostat 100 as described in
more
detail below. In addition to non-volatile memory media, the memory module 254
can also
include volatile memory media (e.g. RAM or FLASH ROM) for storing data,
program
variables and other information required or used by the program.
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[0027] The clock 256 is configured to generate a time-base for the CPU 252 and
also to
generate a real time clock for display on the LCD 230. The input/output module
258
comprises a number of input and output ports. The input/output module 258 is
responsive to the CPU 252 to generate output signals on one or more of the
output
ports. The output ports include an output port for controlling the operation
of the
switching device 222, an output port for writing data to be displayed to the
LCD module
230. The input ports include an input port for receiving voltage/current
readings from the
shunt circuit 224, an input port for receiving temperature data from the
temperature
sensor 250, an input port for receiving keypad signals from the keypad 240.
The analog
module 260 is operatively coupled to the CPU 252 via the ADC 262 and provides
an
interface between the AC line 141 and power module 222. As will be described
in more
detail below, the analog module 260 comprises analog circuits including a zero
crossing
detector. The ADC 262 comprises an analog-to-digital converter which is
operatively
coupled to the CPU 252 and configured to convert an analog input signal (e.g.
AC
voltage and/or current readings from the shunt circuit 224) into a
corresponding digital
signal which is then processed by the program executed by the CPU 252, as will
be
described in more detail below according to an embodiment.
[0028] It will be appreciated that while the control module 210 has been
described as
comprising a CPU, a memory module and other circuit modules or resources, the
control
module 210 may be implemented in the form of a microcontroller with on-chip
resources
comprising the memory, the clock, the input/output module and the ADC.
According to
another embodiment, the control module 210 may be implemented in the form of a
programmable device (e.g. a Field Programmable Gate Array or FPGA) and/or
dedicated hardware circuits.
[0029] Reference is next made to Fig. 3, which shows an implementation of
thermostat
with an energy measurement or consumption calculation mechanism according to
an
embodiment of the invention. The energy measurement mechanism is described in
the
context of the signal processing that is performed by the CPU 252 and
comprises a
number of functions or processes that are executed by the CPU 252 in
conjunction with
the processing or conditioning of signals in the analog module 260 and the ADC
262.
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[0030] As shown in Fig. 3, the analog module 260 includes an input port 310
coupled to
the switching device 222 for inputting line voltage readings, and an input
port 320
coupled to the shunt circuit 224 for inputting line current readings. As
shown, the analog
module 260 includes a signal conditioning circuit 312 configured to condition
the line
voltage readings received at the input port 310. According to an embodiment,
the signal
conditioning circuit 312 comprises an attenuator configured to attenuate the
line voltage
signal to a level suitable for the ADC 262. The conditioned output from the
signal
conditioning circuit 312 is fed to a filter 314. According to an embodiment,
the filter 314
comprises a low pass fifter configured to remove higher frequency noise and
also
alleviate aliasing. The output from the low pass filter 314 is fed to the ADC
262. As
shown, the ADC 262 comprises a two channel device having a first channel 330
for
digitizing the conditioned line voltage signals received from the low pass
filter 314. As
shown, the analog module 260 includes a zero crossing detector circuit
indicated by
reference 316. The zero crossing detector 316 is configured to detect when the
AC line
voltage crosses zero, i.e. transitions between positive/negative and
negative/positive,
and generate an output signal that is coupled to an input port 318 on the CPU
252 for
further processing under the control of the program stored in memory.
[0031] Referring again to Fig. 3, the analog module 260 includes another
signal
conditioning circuit 322 configured to condition the line current readings
received at the
input port 320. According to an embodiment, the signal conditioning circuit
322
comprises an amplifier configured to amplify the line current signal to a
level suitable for
the ADC 262. The conditioned output from the signal conditioning circuit 322
is fed to a
filter 324. According to an embodiment, the filter 324 comprises a low pass
filter
configured to remove higher frequency noise and also alleviate aliasing. The
output from
the low pass filter 324 is fed to a second charmel on the ADC 262 for
digitizing. As
shown, the output, i.e. the digital stream, from the ADC 262 is received by
the CPU 252
at an input port 342.
[0032] According to an embodiment, the CPU 262 executes a function or process
(i.e. in
firmware) to operate the ADC 262 to process one channel at a time. Under the
control of
the function, the CPU 252 closes the switching device 222 to take a line
current
measurement at the input port 320 which is digitized through the second
channel 340 of
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the ADC 262. To take a line voltage measurement, the CPU 252 opens the
switching
device 222 and the line voltage reading at the input port 310 is conditioned
(the signal
conditioning circuit 312) and filtered (the low pass filter 314) and digitized
through the
first channel 330 of the ADC 262 for further processing by the CPU 252.
[0033] As shown in Fig. 3, the CPU 252 is configured with an energy
calculation module
implemented in firmware and indicated generally by reference 350. The energy
calculation module 350 includes a RMS calculation algorithm indicated by
reference 360.
The RMS calculation algorithm 360 is implemented as will be understood by one
skilled
in the art to calculate true RMS values for the line voltage readings 330 and
the line
current readings 332 digitized by the ADC 262. As shown, the RMS calculation
algorithm
360 comprises a processing step 362 for squaring the digitized sample (i.e.
the line
voltage reading or the line current reading). Prior to the squaring operation
362, the
digitized line voltage or line current readings may be passed through a high
pass filter
function as indicated by reference 361. The squaring step 362 is followed by a
summing
operation or step as indicated by 364. In the summing step 364, the squared
value from
step 362 is added to the previous summed value, i.e. Sum = Sum + New Sample.
The
squaring 362 and summing 364 operations are repeated for a number or set of
digitized
readings, and then the summed value is divided by the number of readings as
indicated
by 365. The square root 366 is taken of the result from step 365 to determine
the Root
Mean Square value for measured line voltage or measured line current. For
example,
the RMS (Root Mean Square) value is calculated as follows:
RMS = Square Root((V1*V1 + V2*V2 + V3*V3 +...+ V(n-1)*V(n-1) + Vn*Vn)/n)
As also shown, a low pass filtering operation may be applied as indicated by
reference
367. The CPU 252 then stores the calculated voltage value(s) in a voltage
reading table
390 (or other data structure) in the memory module 254. Similarly, the CPU 252
stores
the calculated current value(s) in a current reading table 392 in the memory
module 254.
[0034] Referring again to Fig. 3, the energy calculation measurement module
350
includes a function or process indicated by reference 370 for calculating
power.
According to an embodiment, the power calculation process 370 comprises a
multiplier
(e.g. implemented in firmware) which takes a calculated voltage measurement
(e.g.
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retrieved from the table 390 in the memory table 390) and multiplies it with a
calculated
current measurement (e.g. retrieved from the table 392 in the memory module
254) to
determine a power consumption value, for example, in Watts or Kilowatts.
According to
another aspect, the energy calculation module 350 includes an integrator
function
indicated by reference 372 for calculating an energy consumption value for the
electric
baseboard heater 102 (Fig. 1). The integrator 372 determines the energy
consumption
(for example, in Kilowatt hours) based on the calculated power value and a
time value or
period. The time value or period for calculating the energy is determined by
the CPU 252
through a time/clock processing function 358. According to another aspect, the
time/clock processing function 358 is configured to determine operating time
intervals
and/or a total time of operation for the electric baseboard heater 102.
[0035] According to an embodiment and as shown in Fig. 3, the CPU 252 is
configured
with a data processing module or component 352, a keypad processing module or
component 354, a temperature processing module or component 356 and a
time/clock
processing module or component 358. According to an embodiment, these module
or
components are implemented as functions or processes in firmware or software
and
comprise executable instructions which are executed by the CPU 252. The data
processing module 352 is configured to process input/output data and control
the overall
operation and functions of the thermostat 100, for example, controlling
operation of the
switching device 222, controlling operation of the ADC 262, executing the RMS
calculation algorithm 360, performing the power calculation 370, performing
the energy
calculation 372, writing data to be displayed to the LDC module 230,
processing key
presses from the keypad module 354, processing temperature measurement from
the
temperature readings module 356, processing time measurements from the
time/clock
module 358. The keypad module 354 is configured to receive and process (i.e.
debounce) the key presses on the keypad 240. The particular implementation
details for
the firmware modules to provide the functionality for the operation of the
thermostat as
described herein win be within the understanding of one skilled in the art.
[0036] According to an embodiment, the data processing module 352 is
configured to
display an ambient temperature reading 231 and a preset (i.e. user)
temperature setting
233 on the LCD module 230. The user uses the keypad 240 to enter the
temperature
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setting and other inputs for controlling the operation or programming of the
thermostat
100. According to another embodiment, the thermostat 100 includes a
programmable
feature, and the data processing module 352 is configured to display the
ambient
temperature reading and one or more preset temperature settings and associated
time
periods. According to another aspect, the data processing module 352 is
configured to
display a real-time clock 235 (e.g. 12 or 24 hour) on the LCD 230.
[0037] According to another aspect, the CPU 252 is configured with a device
rating
module 359. The device rating module 359 is configured to allow a user to
input power
consumption and/or energy rating information or parameters for the electric
baseboard
heater 102, for example, based on the marked rating(s) for the heater 102. The
data
processing module 352 is configured to display these ratings 237, 239 in
addition to
and/or instead of the actual calculated power consumption and energy values.
According
to another aspect, the data processing module 352 is configured with a
function to
compare the actual power and energy consumption values with the rated values.
This
information can then be used to determine whether the heating apparatus is
operating
efficiently, needs to be repaired or replaced, etc. According to an
embodiment, the CPU
252 is configured to execute a function which uses the given heater rating and
the
measured (calculated) power to detect an open circuit condition in the heater
102. For
example, an open circuit condition can occur if the heater 102 is shut down by
a safety
cutoff circuit in response to an unsafe operating condition, such as a dust
buildup or a
disconnected wire. According to another embodiment, the CPU 252 is configured
to
execute a function which monitors one or more heaters 102 (for example,
arranged in a
group) and based on the calculated energy consumption values a determination
(e.g. the
function compares the given heater rating to the total calculated power value)
is made if
one or more of the heaters 102 is faulty or not operating according to its
given rating.
According to another embodiment, the CPU 252 is configured to detect the
"loading" of
the heater 102 based on the calculated energy consumption value, for example,
a heater
which is operating above the given heater rating.
[0038] According to another aspect, the data processing module 352 is
configured to
calculate an estimated cost of operation 238 for the heater over a given time
period on
the basis of the calculated power consumption value stored in memory 394. The
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estimated cost of operation 238 may be displayed on the LCD 230. In a further
embodiment, the thermostat may display a visual warning or emit an auditory
warning if
the estimated cost of operation exceeds a predetermined value.
[0039] In operation, a user enters a desired temperature setting using the
keypad 240.
The temperature setting is stored in the memory module 254, and the CPU 252
executes a function to measure the actual room temperature using the
temperature
sensor 250. If the measured temperature is below the desired user temperature
(i.e. set
point temperature), the CPU 252 controls the switching device 222 to supply
electrical
power to the electric baseboard heater 102 and activate the heating element
104 to heat
the room or physical space. When the switching device 222 is turned on, i.e.
closed, the
CPU 252 can also measure the line current and calculate RMS line current
values which
are then stored in the memory module 254. Similarly, when the switching is
turned off,
i.e. open, the CPU 252 can measure the line voltage and calculate RMS line
voltage
values which are also store in the memory module 254. For example, the CPU 252
is
configured to sample the line voltage and/or the line current at a pre-defined
sampling
interval. The stored line voltage and line current values are then used to
make power
and/or energy calculations, for example, at pre-defined intervals for display
on the LCD
module 110 or in response to a user input (e.g. power or energy key press).
[0040] In a further embodiment, the thermostat may display a visual warning or
emit an
auditory warning if an unsafe operating condition or faulty heater is
detected.
[0041] While the embodiments according to the present application have been
described in the context of a line powered electric baseboard heater, it will
be
appreciated that the embodiments may be extended or find application in other
types of
electrical or line powered devices.
[0042] The present invention may be embodied in other specific forms without
departing
from the spirit or essential characteristics thereof. Certain adaptations and
modifications
of the invention will be obvious to those skilled in the art. Therefore, the
presently
discussed embodiments are considered to be illustrative and not restrictive,
the scope of
the invention being indicated by the appended claims rather than the foregoing
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description, and all changes which come within the meaning and range of
equivalency of
the claims are therefore intended to be embraced therein.
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